In many situations a coolant has to be delivered to a rotary body, for example, to the rollers of a steel slab casting mill where temperatures in excess of 1000.degree. C. are encountered. The required coolant is supplied to the rollers through a rotary joint.
Though the invention will be described with particular reference to the above application (rotary joint delivering coolant water to a slab casting roller) it is to be understood that the invention has general application to situations where a liquid has to be supplied to a rotary body.
To supply coolant to a roller the stationary coolant supply has to be matched to the rotary motion of the roller. Moreover a required relationship has to be maintained between the coolant supply hoses and the rotary joint to reduce wear and prevent obstruction or failure of the supply hoses. The joint therefore has what will henceforth be referred to as a stator component and a rotor component. The stator allows connection to the stationary coolant supply while the rotor accommodates the rotary motion of the roller.
The roller is supported on bearings which require lubrication and this lubricant must be kept isolated from the coolant, which is generally water, to prevent bearing failure or reduced bearing life by contamination. A grease seal is therefore required between the rotor and the stator.
In the prior art these problems have been solved with complex joints exemplified by the rotary joints manufactured by Yamada Industrial Co. Ltd. of Japan and the Deublin Company of the U.S., Germany, and the UK.
One example of the Deublin design is shown schematically in FIG. 1, which shows a two-way water flow joint. The coolant supply is delivered to the rotary body (e.g. roller) along channel 10 surrounding pipe 12 from inlet 14 and returns through pipe 12 to outlet 16 (or vice versa). A one way flow rotary joint is provided by removing pipe 12 and plugging outlet 16. The rotor 18 is attached by threaded pipe to the rotary body. The rotor 18 is supported on ball bearings 20, 22 and sealing is provided by a rotary seal. A rotary seal comprises a rotating ceramic seal 24 in contact with a stationary carbon graphite (or tungsten carbide) seal 26, the latter pressed into and maintained in contact with the rotating seal 24 by a stainless steel wave spring 28. To work, the seal faces must be maintained in contact with a substantially constant force and the faces need to be well mated. To achieve the latter result the seal faces are ground "optically flat" (to better than 0.000023").
Similarly, in the Yamada design as shown schematically in FIG. 2 coolant flows into inlet 40 along pipe 42 and returns within pipe 42 to exit from outlet 44 (or vice versa). A stationary shaft 46 supports the coolant supply head 48 and the rotor which in part comprises outer casing 50. The casing 50 rotates on a cermet dry bearing 52 . The end cover 54 attaches the rotor to the rotary body (roller) with which the joint is to be used. A rotary seal isolates the end cover 54 from the stationary shaft 46 and comprises a "micro-lapped" ceramic stationary seal 56 engaging a rotating "micro-lapped", floating seal 58. The seals 56, 58 are held in contact by spring 60. Again as in the Deublin design precision grinding of the faces of seals 56, 58 is required for effective operation of the seal and thus the joint.
These prior art rotary joints have a large number of parts. Failure of any one of these parts adversely affects the operation of the joint and in time will result in failure of the joint and contribute to failure of the bearings of the roller. In the harsh environment and high temperatures encountered in a slab caster the spring force may not always be optimal or uniform and dirt can work between and proceed to deteriorate the mated faces of the seals. This allows coolant to contaminate the rotary joint bearing(s) inducing bearing failure. In addition the coolant (being under pressure) is forced between any small gaps in the sealing faces (once formed) with great force greatly accelerating the attrition of the sealing faces. Under these conditions the spring may also become weakened by corrosion contributing further to the loss of the required sealing.
In addition both the Yamada and Deublin rotary joints require individual brackets to be made to fix the joint in place onto the bearing housing of the roller. This can be expensive in the case of a steel slab caster where hundreds of rollers are involved of varying sizes and there are normally one or two joints per roller. These joints are also long, a fact which presents a space problem in some applications and involves a large cantilever moment which must be considered when supporting the joint.